1. Field of the Invention
The present invention relates to a medical apparatus provided with a bending portion configured by connecting a plurality of bending pieces to an insertion portion.
2. Description of the Related Art
In recent years, various medical apparatuses have been used to diagnose, extract and treat a living body in a medical field. Examples of such a medical apparatus include an endoscope provided with an observation optical system at a distal end portion thereof and a medical manipulator provided with a hand arm, a knife arm or the like at a distal end portion thereof.
Endoscopes and medical manipulators can be divided into a type with an insertion portion configured to be rigid and a type with an insertion portion provided with a bending portion. The bending portion has, for example, a multi-joint structure with a plurality of substantially ring-shaped bending pieces pivotably connected via connecting pins. The bending portion is configured to bend in two directions, up and down or four directions, up and down, left and right.
Japanese Patent Application Laid-Open Publication No. 2009-89820 and Japanese Patent Application Laid-Open Publication No. 2002-48983 disclose a type with the bending portion made up of a coil spring.
The bending portion formed into a multi-joint structure is configured to be bent by pulling or loosening a bending wire. The distal end portion of the bending wire is fixed to a distal end bending piece making up the distal end of the bending portion. On the other hand, the proximal end portion of the bending wire is fixed to a bending portion operation unit provided in an operation section.
According to this configuration, when bending the bending portion, for example, in an upward direction, an operator turns a rotary operation knob making up the bending portion operation unit in a predetermined direction. An upward bending wire fixed to the distal end bending piece is pulled as the rotary operation knob is turned, while a downward bending wire is loosened and the bending portion is bent in an upward direction.
When restoring the bending portion bent in the upward direction as described above to an original state, that is, an unbent state (also described as “neutral position” or “rectilinear state”), the operator returns the rotary operation knob to the original position, that is, turns the rotary operation knob in a direction opposite to the aforementioned direction. The downward bending wire is then pulled, while the upward bending wire is loosened and the bending portion is restored to the neutral position.
When the bending portion is returned to the neutral position by operating the rotary operation knob, in the bending portion configured by connecting a plurality of bending pieces, responsivity thereof deteriorates as the bending state of the bending portion approaches the neutral position. That is, the bending operation of the bending portion becomes dull relative to the amount of turning of the rotary operation knob. As a result, even when the rotary operation knob was returned to the original position, it was difficult to restore the bending portion to the rectilinear state and restoring it to the neutral position was particularly difficult on the bending portion distal end side. The deterioration of responsivity may be attributable to the fact that the bending wire is given a looseness beforehand and that friction is produced between a bending piece and a connecting pin connecting neighboring bending pieces or the like.
However, what is most important to the operator is that the bending portion performs accurate bending operation through operation of the rotary operation knob and a desired observed image is thereby obtained. Therefore, when the bending operation knob was returned to the original position, the operator did not take notice of whether or not the bending portion was restored to the neutral position.
On the other hand, medical apparatuses developed in recent years such as motor-driven bending endoscopes or motor-driven medical manipulators include a motor-driven bending portion at an insertion portion. A medical apparatus having a motor-driven bending portion is required, when the bending portion operation unit is set to a 0 point (origin), to be set at a neutral position where the bending portion is not bent in any direction, that is, a state in which the front is being observed which is the axial direction of the insertion portion in the case of a front viewing endoscope.
Regarding techniques for returning the bending portion to the neutral position, for example, Japanese Utility Model Laid-Open No. 6-44502 discloses a bending mechanism including a bent portion reconstruction member made of a shape memory alloy arranged inside the bent portion. Furthermore, Japanese Patent Application Laid-Open Publication No. 2008-183420 discloses a flexible endoscope wire spring guide including a coil pipe having reconstructing elasticity provided in a bending portion and a bending wire inserted in the coil pipe.